692 FRANK D. ADAMS 



These sheets of metal were then arranged in an upright posi- 

 tion in a stout wooden frame, one in front of the other, at a distance 

 of one inch apart. That of the rock having the highest content 

 of sihca was placed at one end of the series, while the others were 

 arranged in the order of decreasing silica content, the most basic 

 rock occupying the other end of the series. The spaces between 

 the plates were then filled in with plaster of paris, the plaster 



Fig. 2: — ^Model showing the chemical composition of the various rock types of the 

 petrographical province of the Monteregian Hills. 



between the successive sheets being smoothed down, so that the 

 model thus completed presented a warped surface, passing trans- 

 versely across which can be distinctly seen the traces of the curves 

 representing the composition of the constituent rocks of the series. 

 The model thus obtained is shown in Fig. 2. A margin about 

 one inch in width was left on the silica side of the model, to give 

 space opposite the curve of each analysis to attach a small label 

 having printed on it the name of the rock and the locality from 



